I had the same question. Apparently there are a couple of commands to look at:

  fltmc filters

That shows the filters loaded, and presumably the ones with "num instances" of 0 aren't actually in use on any volumes.

You can figure out what each of the filters is by looking at the output of:

  sc query type=driver

To figure out what the ones I saw in fltmc were, I used this:

  sc query type=driver | grep -A1 -i -e cldflt -e wcifs -e storqos -e filecrypt -e luafv -e npsvctrig -e wof -e fileinfo